[+Cc Jan]
On Tue, Sep 12, 2023 at 08:20:43AM -0600, Chunhai Guo wrote:
> I am encountering a deadlock issue as shown below. There is a commit
> 344150999b7f ("f2fs: fix to avoid potential deadlock") can fix this issue.
> However, from log analysis, it appears that this is more likely a fake
> progress issue similar to commit 68f4c6eba70d ("fs-writeback:
> writeback_sb_inodes: Recalculate 'wrote' according skipped pages"). In each
> writeback iteration, nothing is written, while writeback_sb_inodes()
> increases 'total_wrote' each time, causing an infinite loop. This patch
> fixes this issue by not increasing 'total_wrote' when nothing is written.
>
> wb_writeback fsync (inode-Y)
> blk_start_plug(&plug)
> for (;;) {
> iter i-1: some reqs with page-X added into plug->mq_list // f2fs node page-X with PG_writeback
> filemap_fdatawrite
> __filemap_fdatawrite_range // write inode-Y with sync_mode WB_SYNC_ALL
> do_writepages
> f2fs_write_data_pages
> __f2fs_write_data_pages // wb_sync_req[DATA]++ for WB_SYNC_ALL
> f2fs_write_cache_pages
> f2fs_write_single_data_page
> f2fs_do_write_data_page
> f2fs_outplace_write_data
> f2fs_update_data_blkaddr
> f2fs_wait_on_page_writeback
> wait_on_page_writeback // wait for f2fs node page-X
> iter i:
> progress = __writeback_inodes_wb(wb, work)
> . writeback_sb_inodes
> . __writeback_single_inode // write inode-Y with sync_mode WB_SYNC_NONE
> . . do_writepages
> . . f2fs_write_data_pages
> . . . __f2fs_write_data_pages // skip writepages due to (wb_sync_req[DATA]>0)
> . . . wbc->pages_skipped += get_dirty_pages(inode) // wbc->pages_skipped = 1
> . if (!(inode->i_state & I_DIRTY_ALL)) // i_state = I_SYNC | I_SYNC_QUEUED
> . total_wrote++; // total_wrote = 1
> . requeue_inode // requeue inode-Y to wb->b_dirty queue due to non-zero pages_skipped
> if (progress) // progress = 1
> continue;
> iter i+1:
> queue_io
> // similar process with iter i, infinite for-loop !
> }
> blk_finish_plug(&plug) // flush plug won't be called
>
> Signed-off-by: Chunhai Guo <guochunhai@xxxxxxxx>
> ---
> fs/fs-writeback.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 969ce991b0b0..54cdee906be9 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -1820,6 +1820,7 @@ static long writeback_sb_inodes(struct super_block *sb,
> struct inode *inode = wb_inode(wb->b_io.prev);
> struct bdi_writeback *tmp_wb;
> long wrote;
> + bool is_dirty_before;
>
> if (inode->i_sb != sb) {
> if (work->sb) {
> @@ -1881,6 +1882,7 @@ static long writeback_sb_inodes(struct super_block *sb,
> continue;
> }
> inode->i_state |= I_SYNC;
> + is_dirty_before = inode->i_state & I_DIRTY_ALL;
> wbc_attach_and_unlock_inode(&wbc, inode);
>
> write_chunk = writeback_chunk_size(wb, work);
> @@ -1918,7 +1920,7 @@ static long writeback_sb_inodes(struct super_block *sb,
> */
> tmp_wb = inode_to_wb_and_lock_list(inode);
> spin_lock(&inode->i_lock);
> - if (!(inode->i_state & I_DIRTY_ALL))
> + if (!(inode->i_state & I_DIRTY_ALL) && is_dirty_before)
> total_wrote++;
> requeue_inode(inode, tmp_wb, &wbc);
> inode_sync_complete(inode);
> --
> 2.25.1
>
